Engine cylinders for passenger vehicles may have one or more electrically actuated intake and or exhaust valves. These electrically actuated valves can operate independently of a crankshaft and/or piston position, for example. Various modes of operating these valves may be provided for improving engine control and/or emission reduction.
One approach adjusts relative valve cycles to fire multiple cylinders simultaneously to improve starting. Then, after a predetermined number of working cycles, the simultaneous actuation is terminated. Such an approach is described in U.S. Pat. No. 6,050,231.
However, the inventors herein have recognized a disadvantage with such an approach. For example, while U.S. Pat. No. 6,050,231 may provide increased starting torque for one or more cycles, the engine will be operating in unusual firing order. Further, there is a potential for increased emissions and/or increased torque fluctuations when discontinuing this unusual firing order. This may result in significant customer dissatisfaction or increased catalyst cost to compensate for the excess emissions.
In one approach, at least some of the above disadvantages, or other disadvantages, may be achieved by a method for controlling an engine having at least two cylinders, at least one of which having at least an adjustable valve, the method comprising:
performing a combustion in at least two cylinders having pistons, said combustions for said cylinders occurring during a common stroke of said pistons;
increasing a number of strokes in a cycle of one of said at least two cylinders; and
returning operation of said one of said at least two cylinders to four strokes, so that combustion of said one of said at least two cylinders occurs sequentially from the other of said at least two cylinders. In this way, it may be possible to reduce emissions, for example.
In another approach, at least some of the above disadvantages, or other disadvantages, may be achieved by a method for controlling an engine having at least two cylinders, at least one of which having at least an adjustable valve, the method comprising:
performing a first combustion in at least two cylinders having pistons, said first combustions for said cylinders occurring during a common stroke of said pistons;
decreasing a number of strokes in a cycle of one of said at least two cylinders; and
returning operation of said one of said at least two cylinders to four strokes, so that combustion of said one of said at least two cylinders occurs sequentially from the other of said at least two cylinders. In this way, it may be possible to reduce any lapse in torque pulses to maintain engine speed.
An example advantage that therefore may be achieved is a way to transition from a multiple cylinder firing condition to a fully sequential firing with at least one of reduced emissions and reduced torque fluctuations.